From the viewpoint of the chemical unit operation, the rotary kiln’s operation is a process that how to reasonably handle the heterogeneous heat and mass transfer of solid and gaseous media. The operation technology of this process has high, requirement and has many changeable factors, so the operation is more difficult than the heterogeneous heat and mass transfer process of the gaseous media and liquid.
Material inlets into the kiln from the feed, due to the inclination of kiln body, under the rotation of the kiln, along the axial direction, the material will slowly move from the feed port along the barrel downward the spout, in the horizontal dimension, material will have various movement modes, like the slide and tumble mode. During the movement process of material, it will constantly overturn, leaving the kiln gases and the new material turned up to contact, making the heterogeneous heat and mass transfer operated, and then coming out from the under spout.
According to the chemical changes of material in the respective segment, from head to the inlet, it can be divided into four bands: drying band, preheating zone, firing zone and a cooling zone. Now take the alumina rotary kiln for example, simply describing the physical and chemical reactions of these regions.
1. drying band: the temperature of the material into the kiln is heated from about 40 degrees to 200 degrees, so that making the attached water brought by the aluminum hydroxide in this band evaporated, and the kiln gas temperature is reduced by from 600 degrees to 250 degrees, and then discharged out of kiln.
2, dewatering belt: Material is continually heated from 200 degrees to 900 degrees, the water of crystallization of the aluminum hydroxide is removed and changed into a γ-Al2O3. The kiln temperature is reduced from 1050 degrees to 600 degrees.
3, burning zone: the material is heated from 900 degrees to 1200 degrees, making the γ-AL2O3 transformed into α-AL2O3. Its transformation process depends on the temperature, residence time, and whether to add the mineralizing agent. In this paragraph, the airflow temperature is 1050 degrees to 1400 degrees.
4, cooling zone: the role of the cooling zone is to make the clinker with the pre-secondary air heat exchange, after cooling the clinker, and then further cooling it into the cooling machine.
The length of the entire region is not fixed, it will change with the different specifications of the calcining kiln and operating conditions, but the belt temperature is substantially constant.
